An internetwork of computers typically consists of a geographically distributed collection of interconnected network segments which are connected using routing devices such as routers. A network segment can be a local area network (LAN) or a wide area network (WAN). A LAN is a network of computers in close proximity, such as a network at one corporate office. The various LANs can then be connected together by point-to-point links that form a WAN, such as a WAN connecting all the various different locations of the offices of a company. These numerous LAN and WAN segments connected by routers form a relatively complex topology of the network. Because of such complex topologies of corporate networks, it becomes highly important to accurately monitor the network to ensure proper operation, and to quickly and accurately detect and correct faults in the network.
Network management software provides the ability to control and monitor devices on a computer network from a central location. A managed device can be any type of node residing on a network, such as a computer, printer or router. Simple Network Management Protocol (SNMP) (a part of the TCP/IP protocol suite) is the protocol typically used for the management related communication between the network management software application and the managed devices.
As networks are constantly being modified and expanded with new users, services, and applications, such network management software is a vital tool for a network manager to keep track of the network resources and to allocate the network bandwidth in the most efficient manner. These tools, such as Novell's ZENworks® for example, allow the network manager to allocate bandwidth between users, locations, and applications, and to generally manage network traffic. Typical monitoring services provided by such software include the ability to monitor bandwidth consumption, connection time, response time, and connection failures. Using the software, policy rules can then be defined for the network in order to optimize traffic, and, specifically, the users, services, and times to which the rules apply can also be defined. Moreover, the software can enable the configuration and remote management of routers and switches, as well as other network devices. Accordingly network management systems typically provide functions for fault management (for detecting and notifying the network manager when a failure occurs in network hardware or software), configuration management (for remotely configuring the network devices), accounting (for logging usage of network resources), performance management (for monitoring the performance of the network and the network devices), and network security (for detecting and notifying the network manager of potential misuse of network resources).
Typical network management software also automatically discovers the topology of the network and depicts it in the form of a map. More specifically, typical network management software scans configuration data for the network devices, such as is available in route tables and/or interface lists, in order to discover the arrangement of the devices in the network and the connections between those devices. These devices can include computers, printers, hubs, switches, and routers, and the connections can include network nodes or links between devices. Accurate knowledge of the network topology is important to proper management of the network as well as prediction of the performance of the network. For example, the network management application needs to know the configuration and links in the network in order to manage the network resources, such as shared software application resources and other resources such as memory and printing resources. This knowledge can also help to predict where network traffic may be high, and to plan resources accordingly. Moreover, this knowledge can be helpful in determining the cause and location of faults that may occur on the network.
Because of the complexity of most networks, manual discovery of the network topology for network management purposes would be burdensome and time consuming. Accordingly, automated systems have been developed for network topology discovery utilizing information regarding the various network addresses of the devices in the network. In particular, every device on the network is usually identified by a unique address. If Internet Protocol is used, this address is called the Internet Address (or an IP address). An IP address consists of a network id and a host id. The network id represents the LAN or the WAN segment to which the device belongs. A typical network management application uses the network address of each network segment connected to a router to discover and depict the topology of the network. Such systems have had the capability of identifying the addresses of the various devices on the network as well as the addresses of the interfaces of a given device linking it to other devices in the network. Thus, by automatically identifying the network addresses of the devices, interfaces and links, the topology of the network can be known.
A typical automated topology discovery method would create a network segment S for each interface of a router, the network segment being identified by the network number N of the router interface. Other computers are then said to belong to the network segment S if they have an address belonging to the same network number N as the router interface. Then, if router B contains an address belonging to the same network number N, router B is added to segment S and other segments that belong to B are linked to S through router B.
Previously, the interfaces of a device have been assigned addresses. For instance, each port on a router can be assigned a network address which identifies it. However, recently, a feature has been provided on devices such as routers and servers which allow no address to be assigned or defined for a point-to-point interface (e.g., a communication interface connecting two networks, such as two LAN's of a company in different cities). This feature was intended to counter the scarcity of addresses, as more and more addresses are being used due to the increase in the number of networked devices. In particular, point-to-point traffic flows only to a single destination or peer, and is therefore not being routed to any other destination. Therefore, assigning a unique address to that interface wastes addresses within the address pool allocated for the network. Such interfaces are called unnumbered interfaces and the point-to-point links between two router interferes are called unnumbered links. Unnumbered links can be configured on PPP, frame relay, and X.25 interface types, for example.
Such unnumbered or unaddressed links and interfaces pose a problem to automated network address based topology discovery methods used by network management software applications. In particular, all unnumbered interfaces use a default network address, such as 0.0.0.0. Accordingly, typical automated network discovery methods would fail to distinguish one unnumbered interface of a router from another unnumbered interface, and would fail to properly assign devices to the proper segment or router link. Therefore, accurate information cannot be obtained regarding the network topology.
While other attempts to identify unnumbered interfaces have involved use of the address of the next hop router in the route table, such methods are likewise often not accurate. In particular, many routers from popular vendors like Cisco and Nortel assign a value of 0.0.0.0 to the address of the next hop router (the ipRouteNextHop if SNMP protocol is utilized). Therefore, use of these methods can fail to identify a distinct and meaningful value for an unnumbered interface of a router. Moreover, many discovery methods can also fail to accurately handle changes in the network topology, such as when an unnumbered link fails.
Accordingly, methods and systems for automatically and accurately identifying unnumbered network links are desired.